The present invention relates to a radio communication terminal that cancels radiated noise to improve the transmission performance of radio communication system.
An increase in the clock frequency of a personal computer raises a problem that a clock signal by the personal computer affects a radio communication terminal disposed adjacent hereto for use in combination therewith. This is shown in FIG. 12. In FIG. 12 a base station 10 and a radio communication terminal 20 exchange information over a radio channel 13. In this instance, the radio communication terminal 20 receives, as well, radiated noise NR from a personal computers or similar electronic equipment 30 disposed in close proximity thereto. The radio communication terminal 20 is not only a portable terminal but also a terminal built in electronic equipment (a personal computer), such as a PC card type radio communication terminal incorporated in the personal computer.
In general, a receiver in the radio communication terminal receives an information signal SD shown in FIG. 13, then limits its band with such a filter characteristic as shown in FIG. 14. However, the radiated noise NR superimposed in the same band as that of the information signal SD cannot be cancelled by the filter characteristic 12. Accordingly, the radiated noise NR degrades the transmission quality of the information signal SD.
One possible method to lessen the influence of radiated noise is to locate the receiving antenna away from the radiated noise source, but in particular, when it is built in electronic equipment, no sufficient measures can be taken because of miniaturization of device and ease in attachment of the antenna itself, for instance.
There are still some more interference signals that enter the receiving band. A typical example is an echo. This is a phenomenon that, for example, in a telephone line a transmitted signal leaks from the transmit path back into the receive path by an electrical mismatch between analog telephony devices and transmission media in a portion of the network. The echo degrades the speech quality. To cope with this problem, an echo canceller is available. That is, the echo canceller cancels the unwanted echo by subtracting the expected echo (pseudo echo) estimated from the transmitted signal on the received path.
In contrast thereto, as for the interference caused by the radiated noise, there are still unavailable techniques for generating pseudo radiated noise that corresponds to pseudo echo and, therefore, it is impossible to cancel the radiated noise by use of the echo canceller technology.